Whether it's that vital phone call or the big problem of the day, tackle that important task at the end of the day, especially around 5pm, because your body is primed to concentrate best at that time, says Fast Company.

A Wall Street Journal article found that our working memory, alertness, and concentration all improve with our body temperatures, which increase throughout the day. The link between body temp and cognition shows us that we have all sorts of biological rhythms within us throughout the day.

What we might want to warm up to, then, is that it makes sense to match our tasks to our physiology: our bodies are warmest around midday, meaning that our concentration is awesome then. Plus our lung capacity—another indicator of mental ability—is highest around 5 p.m., so it makes sense to leave some deep work for the end of the day.

At this time, the lungs use oxygen more efficiently, you're more coordinated, and your muscles are warmed up

Some hours of the day are better for some tasks than other. Research suggests, for example, that…
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Now, don't start picking on the specificity of the 5pm time slot. Keep in mind that this is not written in stone, but more a suggestion by which you can figure out when you are feeling at your peak and get things done. Sometimes, you will have had a particularly tiring work day and won't be up to a big task at the end of it. But if you begin the day by scheduling an important assignment for 5pm, you can pace yourself knowing that. It might help you find the "good hours" you should work to become more productive.